1. Field of the Invention
The present invention relates to a shutter apparatus, an image sensing apparatus, and a shutter control method.
2. Description of the Related Art
In a conventional shutter apparatus which is equipped with a stop function and mounted in a silver halide camera, the shutter is released by an operation where a blade member is opened to the degree that an F-number corresponding to the curtain speed (the driving speed of the blade member) is obtained, and immediately closing the blade member. Exposure starts as the blade member starts to open, and the driving direction of the blade member is reversed from the opening direction to the closing direction the moment a predetermined F-number is obtained (see FIG. 8B).
On the other hand, an image sensing apparatus such as a digital camera can shoot an image simply by resetting the charge stored on an image sensor (reset scanning) while the image sensor is exposed, and starting charge storage to move the blade member in the closing direction when it is kept open, without reciprocally moving it.
However, if the time delay from when an instruction to perform the closing operation of the blade member is issued until this closing operation actually starts is relatively long, it is difficult to increase the shutter speed using an arrangement that performs reset scanning with reference to the instruction to perform the closing operation of the blade member.
Japanese Patent Laid-Open No. 2001-337361 describes a technique of detecting, by a sensor, the closing operation of a shutter blade in a shutter apparatus of a digital camera, and setting the exposure start timing in correspondence with the exposure time based on photometric data using the time point, at which this closing operation is detected, as a starting point (see FIG. 8A). The use of the technique described in Japanese Patent Laid-Open No. 2001-337361 allows an increase in shutter speed even if the delay time from when an instruction to perform the closing operation of the blade member is issued until this closing operation actually starts is relatively long.
Unfortunately, the technique described in Japanese Patent Laid-Open No. 2001-337361 mentioned above requires a sensor which detects the closing operation of the shutter blade, separately from a shutter mechanism or a shutter driving mechanism.